AIM:To investigate the expression of miR-23a and epithelial splicing regulatory protein 1(ESRP1) in rectal cancer tissues and cell lines as well as their effects on rectal cancer cell viability and apoptosis.METHODS:The relative levels of miR-23a in the rectal cancer tissues and cultured cells were assessed by RT-qPCR.The positive expression of ESRP1 in the rectal cancer tissues and non-cancer tissues was detected by immunohistochemical staining.The sequences of miR-23a inhibitor and inhibitor negative control (NC) were synthesized, and transfected into the SW480 cells.The cell viability was measured by CCK-8 assay.The apoptotic rate was analyzed by flow cytometry.The cell invasion was evaluated by Matrigel counting assay.The expression of ESRP1 was determined by Western blot.The wild-type pGL3-ESRP1-3'UTR (wt-pGL3-ESRP1-3'UTR) or mutant pGL3-ESRP1-3'UTR (mut-pGL3-ESRP1-3'UTR) plasmid and miR-23a inhibitor or inhibitor NC were co-transfected into the HEK293 and SW480 cells.The dual luciferase activity was detected according to Promega dual luciferase reporter gene assay kit instructions.The cell viability and apoptosis were evaluated by CCK-8 assay and flow cytometry analysis, respectively, after the SW480 cells were transfected with ESRP1 mimic or mimic NC.The expression of ESRP1, caspase-3, Smac and X-linked inhibitor of apoptosis protein (XIAP) in the SW480 cells was detected by Western blot.RESULTS:The expression of miR-23a was significantly up-re-gulated in the rectal cancer tissues and cell lines, while the positive expression of ESRP1 was significantly decreased in the rectal cancer specimens.The miR-23a expression was also closely related to lymphnode metastasis and TNM stages of rectal cancer patients.ESRP1 was inversely correlated with miR-23a in the rectal cancer tissues.After transfection with miR-23a inhibitor in human rectal cancer SW480 cells, the down-regulation of miR-23a induced significant inhibition of cell viability as compared with the cells transfected with inhibitor NC (P<0.01).Furthermore, the apoptotic rate induced by the miR-23a inhibitor transfection was markedly higher than that of control (P<0.01).Luciferase assay showed that ESRP1 was a direct target gene of miR-23a.The cell viability and apoptosis were inhibited and promoted, respectively, after transfection with ESRP1 mimic in the SW480 cells.Promoted expression of ESRP1 significantly up-regulated the levels of caspase-3 and Smac as well as down-regulated the expression of XIAP in the SW480 cells.CONCLUSION:The expression of miR-23a is significantly associated with the growth and apoptosis of human rectal cancer cells by targeting ESRP1.miR-23a may be a potential therapeutic target for the treatment of rectal cancer in the future.